1. Field of the Invention
The present invention relates to a valve for a control muffler placed in an open end of an exhaust pipe in a muffler or the like, to be opened and closed so as to maintain exhaust pressure of a muffler chamber on the upstream side, to a predetermined value or smaller.
2. Description of the Related Art
Conventionally, an exhaust gas pressure sensitive control muffler is configured in the following manner. During a low engine speed period when the exhaust gas pressure is low, the pressure of the exhaust gas flowing from an inlet pipe P1 into the muffler M is low. Therefore, a countermeasure against noises is taken so that, as shown in FIG. 5, therefore, a closed state of a valve element 3 is maintained by the urging force of a torsion coil spring as indicated by a solid line in the figure to allow the exhaust gas flowing from the inlet pipe P1 to flow through an inner pipe P2 and then be discharged to the outside from an outlet pipe P3, and a small chamber on the upstream side from an inner pipe 1 serves as resonant chamber.
By contrast, when the engine speed is increased and the pressure of the small chamber on the upstream side from the inner pipe 1 exceeds the urging force of the torsion coil spring, the valve element 3 enters an opened state as indicated by the one-dot chain line in the figure to allow the exhaust gas to flow through a flow path elongating from an inner pipe P4 to the inner pipe 1, so that the small chamber on the upstream side from the inner pipe 1 serves as an expansion chamber to lower the back pressure at a high speed.
As a valve which is used in a muffler of this kind, known is a valve shown in FIG. 6. This valve is placed at the downstream end of the inner pipe (exhaust pipe) 1 through which small chambers in the muffler M are connected to each other. The valve element 3 is swingably supported via a bush (bearing) 6 by a support shaft 5 which is welded and fixed to a first shaft supporting portion 41 protruding from a peripheral edge of the downstream end of the inner pipe 1, and urged in a valve closing direction by a torsion coil spring which is not shown.
The bush 6 is formed by using stainless steel wire mesh, and configured by a cylindrical main portion 61 having a smaller diameter and a flange portion 62 having a larger diameter. The bush is assembled so that the cylindrical main portion 61 is pressingly inserted into a bush attaching portion 34 which is formed on a second shaft supporting portion 33 of the valve element 3 so as to be inwardly directed, and the flange portion 62 is interposed between the first shaft supporting portion 41 and the second shaft supporting portion 33. The bush has a structure in which, when the valve element 3 is swung, a shaft hole 63 slides over the outer peripheral face of the support shaft 5.
In the valve for a control muffler of the conventional art, however, it is highly probable that, when the support shaft 5 is welded to the first shaft supporting portion 41 in a process of assembling the valve, as shown in FIG. 7, a weld metal 8 of a welded portion reaches the bush 6 via a shaft hole 41a of the first shaft supporting portion 41 and the bush 6 is fixed to the first shaft supporting portion 41. When the valve element 3 is swung under this state, the outer peripheral face of the bush 6 and the inner peripheral face of the bush attaching portion 34 slide over each other in a pressingly contacted condition. As a result, the swinging operation of the valve element 3 is hindered so that the valve cannot be smoothly opened and closed. Furthermore, an excessive surface pressure is applied to the bush 6, so that the bush 6 largely wears and easily cracks. Consequently, there arise problems in that a valve for a control muffler in which the durability is poor and the useful life is short is produced, and that the production yield is low.
It is an object of the invention to provide a valve for a control muffler in which, when a support shaft is to be welded to a shaft supporting portion in a process of assembling the valve, fixation between the shaft supporting portion and a bearing due to a weld metal can be surely avoided and the production yield is improved.
In order to solve the problem, the valve for a control muffler according to a first aspect of the invention is a valve for a control muffler in which the valve comprises: a valve seat which is placed in an open end of an exhaust pipe in a muffler; a support shaft supported by shaft holes of a pair of first shaft supporting portions which are disposed in close proximity to the open end of the exhaust pipe; a valve element which is swingably journaled on the support shaft inside the pair of first shaft supporting portions; bearings which are respectively interposed between the support shaft and a pair of second shaft supporting portions that are disposed on the valve element to pivotally support the support shaft; and urging member for urging the valve element in a valve closing direction, and, during a low engine speed period, the valve element is caused by an urging force of the urging member to maintain an abutting state with respect to the valve seat, thereby closing the exhaust pipe, and, during a high engine speed period, the valve element is caused by an exhaust gas pressure to open the exhaust pipe, wherein a welding protrusion which protrudes in an axial direction is disposed on an outer opening edge of the shaft hole of at least one of the pair of first shaft supporting portions, and the support shaft is welded to the welding protrusion.
According to a second aspect of the invention, an engagement portion is disposed on a side of one end of the support shaft, the engagement portion abutting against the opening edge of the shaft hole of the first shaft supporting portion, to prevent the support shaft from being inward moved.
In the valve for a control muffler according to the first aspect of the invention, the support shaft is welded to the welding protrusion which protrudes in the axial direction from the outer opening edge of the shaft hole of the first shaft supporting portion. Therefore, the welding point is located in a position separated from the bearing, and hence a weld metal of a welded portion does not reach the bearing, thereby attaining an effect that welding between the first shaft supporting portion and the bearing can be surely avoided. According to the invention, consequently it is possible to obtain a valve for a control muffler which can be produced with a high yield.
In the valve for a control muffler according to the second aspect of the invention, when the support shaft is passed through the shaft holes of the first shaft supporting portions in a process of assembling the valve, the engagement portion abuts against the opening edge of the shaft hole of the first shaft supporting portion on the insertion side, thereby obtaining a state where the inward movement in the axial direction is blocked. When the support shaft is to be then welded to the first shaft supporting portion, therefore, the movement of the support shaft in the axial direction can be completely blocked by setting a state where the engagement portion is upward directed, or pressing the engagement portion toward the first shaft supporting portion with fingers. Consequently, the support shaft can be positioned easily and correctly, thereby attaining an effect that the workability of welding the support shaft is improved.